Friction elements



i atent Ofiice Patented Aug. 25, 1959.

FRICTION ELEMENTS Ray E. Spokes, Ann Arbor, Mich, and John B. Little-.field, Monsey, N.Y., assignors to American Brake Shoe Company, NewYork, N.Y., .a corporation of Delaware No Drawing. Application March 1,1955 SerialNo. 91,510

3 Claims. (Cl. 260--41.5)

This invention relates to a friction element in the form of acomposition brake shoe for braking railway equipment.

The conventional brake shoe utilized with railway equipment has been oneof cast iron applied with radial clamping force directly to the tread ofthe wheel, but there have been proposals of composition shoes consistingof molded or pressed composition material. Such shoes in one formembodied a relatively high proportion of metallic particles togetherwith additional filler such as fibrous asbestos, and these fillers weremixed in a binder matrix of a natural resin or the like. The compositionwas then shaped in to desired form and then cured under heat andpressure; and in some instances the composition was pressed in to anarcuately configured shell or casing serving as a backing, and finallyset to an operative state.

Advantages have been stressed with regard to composition brake shoes ofthe foregoing kind, but regardless of this cast iron shoes prevail todayas the customary friction element for braking railway equipment.

Among the disadvantages of composition or filled shoes of the foregoingkind have been variations in wear characteristics and lack of resistanceto shock which contributed to relatively poor life of the shoes inservice. Moreover, the coefficient of friction of these compositionrailway brake shoes under wet conditions does not compare favorably tothe coefiicient of friction under'dry con ditions, that is, whilefriction is good so long as the shoe is dry there is an unfavorable lowvalue in those instances where the shoe is Wet, this apparently being aninherent defect not encountered with cast iron shoes.

The advantages stressed for a composition railway brake shoe could be ofpractical merit if the aforementioned disadvantages were not present,and in view of this the primary object of the present invention is toimpart to a composition railway brake shoe desirable frictioncharacteristics such that the coefficient of friction under wetconditions compares favorably to that of the shoe when dry and toachieve this desirable relation of frictional characteristics in acomposition railway brake shoe, while at the same time imparting highheat resistance thereto and marked ability to absorb physical shockconsonant with the severe conditions encountered in the deceleration ofrailway equipment.

Another object of the present invention is to achieve-a desirablebalance between wet and dry friction in a friction element byincorporating therein a mineral filler in the form of an aluminumsilicate of the sillimanite group which imparts this desirablecharacteristic to the friction element regardless of other fillers whichmay or may not be resorted to for other purposes.

It has been proposed to include a substantial quantity of metalparticles in composition railway brake shoes. The frictional heatengendered in decelerating railway equipment is of appreciablemagnitude, and it is probable that one of the reasons why compositionrailway brake shoes when embodying an excessive amount of metalparticles-have not been considered entirely satisfactory has been thatthe metal particles, usually of iron, sometimes become incandescent oreven partially fused during braking, thereby tending to weaken and causethermal break-down of the organic binder material and to disrupt theadhesive forces that bind the metal particles in the matrix. What ismore, assertions have been made and evidence shows that the severeheating conditions arising during use of composition railway brake shoescontaining metal particles have accounted for scoring, heatchecking, andundue wear of the wheel tread and poor life of the shoe.

There are advantages to incorporating metal particles in a compositionrailway brake shoe, chief among these being satisfactory friction andthe resistance to wear inherently possessed by such metal filler,especially-iftthe metal be in the form of hard cast iron particles.Accordingly, a further object of the present inventionis to so modify acomposition railway brake shoe containing hard metal particles, such ascast iron particles, that the tendency towardoverheating orincandescence of such hard metal particles is retarded, thus suppressingthe tendency toward disruption and thermal breakdown of the binder andconditions that have a deleterious effect on the wheel tread and thebrake shoe; and a further it object is .to achieve this desirableattribute by an inorganic, filler in the form of a particular aluminumsilicate possessing high heat resistance and capable ofsynergisticallycooperating with the metal filler particles to impart to the brake shoelong life from the standpoint of wear, the abilityto conduct heat awayfrom the face of the shoe, and a coeflicient of friction that issatisfactory under both wet and dry conditions.

High friction by itself can be attained with-relative ease in acomposition railway brake shoe, but the supervening factor which may notbe disregarded is that the value of braking friction must in everysituation be less than the coefiicient of adhesion between the Wheeltread and the rail, for otherwise the wheel will lock during braking andskid on-the rail causing the wheel tread to wear flat. Because of itsgood frictional characteristics and high resistance to Wear, it isadvantageous to include cast iron particles in a composition railwaybrake shoe, but particularly whenbraking at high speeds cast irontendstoward an overbalance between brake friction and adhesion of the wheeltothe rail. A feature ofthe present invention is that cast iron as afiller in a composition brake shoe can be replaced in whole or in partby a filler to be described that has equivalent friction and resistanceto wear While not partaking of undue increase in friction at high speedstending toward the overbalance mentioned as characteristic of cast ironin excessive amounts, and so to do is one of the more important objectsof the present invention.

Specifically, it is an object of the present invention to achieve theforegoing by resort to an inorganic filler material in the form of analuminum silicate selected from the group of minerals consisting ofnaturally occurring kyanite, sillimanite, andalusite, dumortierite andtopaz, the calcination product of these commonly known as mullite, allof which are essentially aluminum silicates, and synthetic forms of theforegoing aluminum silicates of the group hereinafter disclosed, eitheralone, or preferably combined with hard ferrous metal particlessuchas-white cast iron particles in a binder matrix of heat stable rubberselected from the group consisting of heat stable synthetic rubberpolymers and copolymers, and heat stable forms of natural latexrubber,and suitable modifications or variations of these.

Other and further objects of the present invention will be apparent fromthe following description and claims which, by way of illustration setforth preferred embodiments of the present invention and theprinciples'thereofi' and what we now consider to be the best mode inwhich we have contemplated applying those principles. Other embodimentsof the invention embodying the same or equivalentprinciples may be usedand changes may be made as desiredby those skilled in the art withoutdeparting from the present invention and the purview of the appendedclaims.

It has heretofore been proposed that asbestos fibers be used as a fillerin composition railway brake shoes. Asbestos fibers when so used havenot been found altogether satisfactory, because at the high thermalconditions encountered in decelerating railway equipment, asbestos losesits water of hydration and the fibers break down into elemental abrasiveparticles readily releasable from the body of the shoe. The manifestresult is a consequent scouring or abrading action by these looseabrasive particles not only on the wheel tread but also on the face ofthe brake shoe. It has been asserted that advantage may be taken. ofasbestos in critically particulate form as a filler enhancing wetfriction of certain brake shoes having limited application, and it wasfurther stated in this same connection that rottenstone, which is a rockof aggregate mineral grains, and diatomaceous earth when of the samecritical particle size were equivalent to asbestos. Cognizance was takeneven in this instance of the abrading action of the particulate fillersproposed, but it is for this very reason that a filler of this kind isnot satisfactory in a railway brake shoe since the life of both thewheel and the shoe is materially lessened to an impractical degree.Moreover, it is known that asbestos does not impart the degree of wetfriction necessary for a railway brake shoe where it is desirous thatsuch a property be alforded.

We have found that the objects set forth above as desirable in acomposition friction element, especially in the form of a brake shoe forrailway equipment, can be achieved and the difficulties heretoforeencountered overcome by having resort to a filler in the form of one ormore aluminum silicates of the group consisting of the so-calledkyanite-sillimanite group of naturally occurring minerals includingkyanite, sillimanite (including Detrital kyanite-sillimaniteconcentrate) and andalusite and the closely related minerals of similarcomposition, namely, topaz and dumortierite. The first three of theaforesaid naturally occurring minerals, namely, kyanite, sillimanite andandalusite, subscribe to the general quantitative formula Al SiODumortierite has the general formula 8Al O .B O .6SiO .H O, and topazthe general formula Al (FOH) SiO Each is inherently of highly refractorynature, that is, displays a very high degree of heat resistance.Accordingly, an aluminum silicate of the group referred to above, whenused in accordance with the present invention as an inorganic mineralfiller for a composition friction element, does not partake ofincandescence which is a characteristic of metal fillers in acomposition friction element.

In addition to displaying the desirable refractory quality of heatresistance, an aluminum silicate of the group hereinabove referred toexhibits a high degree of hardness or wear resistance such as to comparefavorably to hard ferrous metal particles used heretofore as a hardfiller in composition friction elements. Of primary importance is thatthe aluminum silicates of the group of materials hereinabove referred towhen used as a filler in a composition friction element impart thereto aWet friction that compares satisfactorily to the friction of the shoewhen dry, and moreover, said aluminum silicates have been found not topartake of increased friction when braking at high wheel speeds which isone objection to cast iron filler material used in excessive quantitiesor in appreciable quantity as the sole friction enhancing agent. Incontradistinction to particulate asbestos, finely divided rottenstone orthe like, the aluminum silicates of the aforesaid group do not scour thecar wheel or act'to self-eiface the wear surface of the shoe.

Of the group of minerals found useful in the practice of the presentinvention, calcined kyanite is the preferred species for the reason thatthis is the most readily available in large quantities. The naturallyoccurring members of the group exhibit certain similar chemical andphysical characteristics as to composition, hardness and resistance tochemical action, and the appearance of these is manifest primarily inlarge, flat blade or needlelike prismatic crystal agglomerations. Themajority of the members of the group undergo transformation at hightemperatures to the needle-like aluminum silicate known as mullite, 3AlO .2SiO crystallizing in the rhombic system. This mineral is quitesimilar physically to sillimanite, and in this connection mullite isreported by some authorities as 2Al SiO .Al O Accordingly, in someinstances it may be advantageous to calcine one of the naturallyoccurring forms of the group to obtain mullite which is the most stableof the six forms. Moreover, synthetic production of mullite has now beenaccomplished by bringing together silica and alumina in combiningenvironment. It will therefore be recognized that the several forms ofthe members of the mineral group referred to above, namely, natural,calcined, or synthetic may be utilized in accordance with the presentinvention.

All members of the aforesaid mineral group are particularlycharacterized by chemical and physical stability at elevatedtemperatures. Thus, kyanite when calcined begins to decompose ortransform to mullite at about 1325 C., andalusite at about 1350 C., andsillimanite at about 1530 C. The product of calcination, mullite, isstable at least up to 1810 C. Dumortierite is stable up to at about 1550C. and topaz up to at about 1000 C.

During calcination, kyanite, sillimanite and andalusite exhibit adecrease in density and accordingly an increase in volume, but except inthe instance of kyanite this physical change is not of any appreciablemagnitude.

Andalusite crystallizes in the orthorhombic system, developingrelatively coarse prisms of practically square cross-section. Thecrystals, however, are roughly developed as a rule and rude columnarmasses are common. It exhibits distinct cleavage, and has a hardness of7.5.

Kyanite is triclinic, and displays good cleavage. It is usually found inlong bladed crystals or columnar to fibrous structure and has. ahardness varying considerably from 5 to 7.25, depending uponcrystallographic direction.

Sillimanite occurs usually as long, slender, needle-like orthorhombicprisms, often aggregated together to form fibrous or compact masses. Itdisplays perfect cleavage and has ahardness of 6 to 7.

Dumortierite, like sillimanite, crystallizes in the rhombic system andoccurs naturally as fibrous or columnar aggregates. It has a hardness of7.

Topaz occurs also as orthorhombic crystals, being prismatic in habit,and possesses a characteristic perfect cleavage. Its hardness is 8.

The characteristics of friction and the heat and wear resistance of thealuminum silicatesof the hereinabove ldisclosed group in a compositionfriction element are independent of the other fillers that mayadvantageously be present, and hence may be used alone or combined withsuch other fillers which independently possess desirable attributes.This feature of the present invention is particularly advantageous sinceby combining the aluminum silicate filler with a long-wearing metallicfiller which is heat conductive, assurance can be had that duringbraking of railway equipment the heat engendered will be conducted awayfrom the wear face of the friction element so that there will be nolocal concentration of heat at the tread of the car wheel. Of particularimportance in the present instance is the fact that the above identifiedaluminum silicate minerals do not break down at temperatures commonlyencountered in the deceleration of railway equipment incontradistinction to asbestos fibers or the like which under similarconditions are high;

ly susceptible totransformation' toabrasive powders tending to scour orunduly Wear the tread of the car wheel. These same aluminunr silicateminerals are distinguishable in the present instance from mineralcarbonates which are relatively soft in nature and which break down atrelatively low temperatures and are unsatisfactory for thepurposes ofthe-present invention.

Preferably, then, in accordance with thepresent invention, the selectedaluminum silicate, or silicates, of the group herein described arecombined synergistically in about equal proportion by weight withcomminuted metallic filler, preferably particles of white cast iron,which possesses an optimum characteristic of long wear and relativelygood heat conduction. Bycombining the mineral and metal filler in thismanner, the two cooperate to aiford a high degree of heat resistance andat the same time a degree of heat conductionthereby eliminating thetendency toward overheating werea metallic filler such as cast ironparticles alone to be resortedto asthe material required to impart thenecessary wear resistance to the composition friction element.

In accordance with prior practice as represented by United StatesPatents Nos. 2,052,779 and 2,267,803, inorganic and organic frictionstabilizers, modifers and enchancersmay be advantageously presenttogether with the aluminum silicate and white cast iron particles. Suchadditional filler materials are preferably represented by lead, leadsulphide, and organic or primarily carbonaceous friction-enhancingmaterial of which petroleum coke is an example. Lead and lead sulphideimpart desir able friction stabilizing action andnon-fade-characteristies to the friction element of the presentinvention, and an organic or carbonaceous filler material such aspetroleum coke alone or together with shredded soft rubber particlesserves to increase or enhance friction particularly at low brakeengaging pressures.

It is important that the binder employed be such as to displayrelativelyhigh resistance to thermal decomposition while at the same time beingstrongly resistant to the relatively heavy shocks and forces engenderedduring the deceleration of railway equipment. A binder of this kind isparticularly manifest in heat stable synthetic copolymer rubber of theBuna-S type, that is, a rubber derived as the copolymerization productof butadiene and styrene, as will be described. A Buna-S binder is ofrelatively flexible nature as compared to shock-sensitive phenolics ofthe phenol-aldehyde type that have heretofore been employed incomposition friction elements, and while flexible synthetic elastomerrubber binders of the Buna-S type have not been viewed as possessingthermal resistance equivalent to phenolics which in fact are infusible,nevertheless, insofar as the braking of railway equipment with thefriction element of the present invention is concerned, a heat resistantrelatively soft elastomer binder of the Buna-S type performssatisfactorily, and such-may be modified if desired with a cashew nutshell liquid polymer binder Which, in fully cured condition, iscross-linked. Moreover, it will be borne in mind that present in therubber binder matrix, in accordance with the present: invention, is thehighly refractory aluminum silicate filler.

Specification of a binder of the Buna-S type is by Way of example only,since the primary consideration in this connection is that a relativelysoft or flexible heat stable binder be used in contradistinction torelatively brittle and infusible phenolics. Accordingly, any of the.natural or synthetic rubbers Which are vulcanizable to a nonthermoplastic or heat stable state may be used, among these beingBuna-S, as noted, Buna-N, Butyl rubber, butadiene acryonitrile (Hycar),reclaimed natural rubber, and heat stable variations of these.

It is further of advantage in some instances to modify the relativelysoft rubber binder with cashew nut shell liquid polymer subsequentlycured or advanced in accordance with conventional procedures with aboutsix percent hexamethylenetetramine during vulcanization of the rubberbinder. Moreover, the cashew'nut shell liquid polymer in the uncuredstate or incompletely set-up stage assists in milling the rubber, aswill be described, and serves also as anextender forspreading the rubberbinder uniformly through the body of filler material. To provide theseadvantages, the cashewnut shell polymer is initiallyused in apreliminary or intermediate stageof heat polymerization, and then isadvanced during the cure of the composition to astage manifest in abenzol extractive test of but fifteenpercent after a sixteen hourextraction test period.

Generally. speaking, the composition railway brake shoe. of the presentinvention, exclusive of solvent; com.- prises from lO'up to about twentypercent by Weight of hard ferrousmetal inthe form of White cast ironparticles; about ten percent by weight or above ofcomminuted aluminum:silicate; about twenty to forty percent by-weight of organic orcarbonaceous friction-enhancing filler material, as representedQforexample, by petroleum coke alone or combined with other organic frictionmate rial;: about 15 to 20 percent lead sulfide; a--rela.tively minorproportion of finely dividedlead; and a synthetic elastomer or rubber:binder in an operative proportion, generally about 12.2 to about 15percentyby weight of the composition, based ontheforegoing, exclusiveofthe vulcanizers and accelerators used to set and cure the bond. Insome instances a minor amount of asbestos fibers. may beused to theextent that additional body reinforcement is attained. Wide variationsare tolerable. For instance, the percentage of cast iron particles maybe increased withacorresponding decrease in the amount of frictionstabilizer and enhancer as Will be described, but operative frictionelements may be made according to the formulae set forth in thefollowing examples in which allparts indicated are by weight:

Example (Parts by Weight) Material I II III Binder (A) 15 r 12. 2Binder1(B) 13.0 White Cast Iron Particles (6-120) 10. 0 20.0 CalcinedKyanite 10. 0 13. 0 12. 0 Lead Sulfide 19. 5 I 22. 2 15.0. Lead 4. G 5.65. 5 Calcined Petroleum Coke 21. fi 39. 3 a 25. 8 Asbestos (Grade 4K)10. 8 Curing Agents:

Litharge 3.4 2 7 3. 2 Zinc Oxide 5. 1 4 2 4.7 A 0 8 0.8 Naptha (solven9.4 9 0 6.7

Example IV A BINDER Ingredient Parts by Weight Buna-S (23%% Styrene)44.0 Cashew Nut Shell Liquid Polymer (Intermediate stage of heat growth)44.0 Rubber Cure:

Sulphur 8. 8 Benzothiazol Disulfide 0. 91 Copper DimethylDithiocarbamate 0. 46 Hexamethylenetetramine l. 83

Example V B BINDER Ingredient Parts by Weight Buna-S (3% tyrene; 8%cumene hydroperoxide) 63.8 Rubber Cure:

Litharge 14. 4 Zinc Oxide 2.18

The particle size'of the filler materials is not critical. Lead, leadsulfide and petroleum coke may be used in powder or like condition ofsub-division and the cast iron particles and filler of the sillimanitegroup may vary between 30 and 100 mesh, about 80 mesh being preferred.

In producing friction elements in accordance with Examples I and IIbonded by the binder of Example IV, the rubber and cashew nut shellliquid polymer in a preliminary or uncured state are first workedtogether intimately in a mill after which the ingredients used tovulcanize, cure and set the binder and advance the liquid polymer areadded thereto and the mixture transferred to a blade mixer. The napthasolvent is then added to the ingredients affording the bond, the mixtureagitated until a paste condition is obtained and then are added thefillers including the castiron particles, aluminum silicate, thefriction modifer and enhancer and the asbestos where such is to be usedfor enhancing body strength. Mixing is continued until a uniformcomposition is attained.

It will be noted that the Buna-S type binder of Example IV undergoesvulcanization by sulfur. After removal of solvent from the compositionmixture at a temperature below that at which vulcanization commences(150 F.), the resulting composition is pressed to shape and the bond issulfur-vulcanized, cured and set under heat and pressure, preferably twotons per square inch for three hours at a temperature of 350 F.,followed by an oven cure for six hours at 350 F. and then an additionaloven cure for twenty-four hours at 500 F. Such cure to produceultimately the friction element of the present invention is, of course,carried out as a molding operation known in the art.

It will be noted that vulcanization of the bond of Example V is one ofcatalysis promoted by cumene hydroperoxide. In preparing a compositionfriction element from this bond in accordance with Example III, theperoxide catalyst is added to the rubber after preliminary milling.Milling is continued to disperse the catalyst, and the litharge and zincoxide accelerators are then added and dispersed. The bonding material istransferred to a blade mixer, solvent is added and a paste preparedafter which the filler materials are added and uniformly dispersed asdescribed above. Solvent is removed at a temperature below that at whichthe bond ingredients normally commence reaction (150 F.), and thecomposition is pressed to shape and thereupon the cure is commenced witha pressure of about two tons per square inch at a temperature of 350 F.for three hours. This preliminary cure is followed by an oven cure forsix hours at 350 F., a second oven cure for twenty-four hours at 350 to490 F., and a final oven cure for forty-eight hours at 490 F. In thisinstance, the elastomer binder is somewhat softer than in the foregoingexample, this being due, of course, to the absence of the cashew nutshell liquid polymer which, in accord ance with the foregoing example,cures to a relatively hard and infusible condition.

Relatively wide variations are possible. Based on Example I, forinstance, we have found that the amount of cast iron particles may beincreased to twenty parts by weight with a corresponding adjustingreduction of ten parts by weight (total) of petroleum coke and leadsulfide, the proportion of binder ingredients and filler includingcalcined kyanite, lead and asbestos, where used, remaining substantiallyconstant. The curing and molding cycle and procedure in this instancebeing as aforesaid.

It will be appreciated that the foregoing are but exemplary embodimentsof the invention illustrative of the '8 compatibility and utilityof analuminum silicate filler of the group herein disclosed with otherfillers as heretofore known and used in composition friction elements.

It is to be understood that while the so-called sillimanite orkyanite-sillimanite group of minerals'consists of naturally occurringkynite, sillimanite and andalusite, the transformation product of theseminerals, known as mullite, and the synthetic forms of these naturallyoccurring minerals, the closely related group of minerals, namely, topazand dumortierite are for the purposes of the present invention, includedwithin the term sillimanite group, and hence this designation as usedhereinbefore and as used hereinafter in the claims is to be construed asembracing any and all of these materials or mixtures thereof.

The resultant friction elements of the present invention achieve theobjects desired in that friction is satisfactory under both wet and dryconditions, wear resistance is high, resistance to both chemical andphysical decomposition is pronounced and satisfactory, and no undueoverheating will be encountered.

Thus, while we have described the preferred embodiments of ourinvention, it is to be understood that these are capable of variationand modification, and we therefore do not wish to be limited to theprecise details set forth, but desire to avail ourselves of such changesand alterations as fall within the purview of the following claims.

We claim:

1. A pressed and molded composition friction element displayingsubstantially equal wet and dry friction and consisting essentially of anon-metallic organic binder matrix subject to thermal decomposition andaifording the main body of the friction element, and hard fillerparticles dispersed uniformly throughout said matrix and affording theessential wet-dry friction equivalence; said filler particles inproportions consisting essentially of about ten to twenty percent byweight of the shoe of heat conductive cast iron particles which tend toincandesce at high temperatures engendered by friction and which serveto conduct heat engendered by friction away from the Wear face of thefriction element, and in addition about ten percent by weight of arefractory heat insulating aluminum silicate selected from the groupconsisting of kyanite, sillimanite, andalusite, dumortierite, topaz andmullite, said aluminum silicate particles serving as heat insulatingbodies among the cast iron particles tending to suppress the thermaldecomposing effect of the incandescible cast iron particles on theorganic binder matrix; and said organic binder matrix consistingessentially of a heat stable rubber.

2. A friction element according to claim 1 wherein the binder matrix ispresent in an amount of about twelve to fifteen percent by weight of thefriction element.

I 3. A friction element according to claim 1 which additionally includesabout fifteen to twenty percent by weight of lead sufide and abouttwenty to forty percent by weight of carbonaceous material.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS AND MOLDED COMPOSITION FRICTION ELEMENT DISPLAYINGSUBSTANTIALLY EQUAL WET AND DRY FRICTION AND CONSISTING ESSENTIALLY OF ANON-METALLIC ORGANIC BINDER MATRIX SUBJECT TO THERMAL DECOMPOSITION ANDAFFORDING THE MAIN BODY OF THE FRICTION ELEMENT, AND HARD FILTERPARTICLES DISPERSED UNIFORMLY THROUGHOUT SAID MATRIX AND AFFORDING THEESSENTIAL WET-DRY FRICTION EQUIVALENT; SAID FILLER PARTICLES INPROPORTION CONSISTING ESSENTIALLY OF ABOUT TEN TO TWENTY PERCENT BYWEIGHT OF THE SHOE OF HEAT CONDUCTIVE CAST IRON PARTICLES WHICH TEND TOINCANDESCE AT HIGH TEMPERATURES ENGENDERED BY FRICTION AND WHICH SERVETO CONDUCT HEAT ENGENDERED BY FRICTION AWAY FROM THE WEAR FACE OF THEFRICTION ELEMEN, AND IN ADDITION ABOUT TEN PERCENT BY WEIGHT OF AREFRACTORY HEAT INSULATING ALUMINUM SILICATE SELECTED FROM THE GROUPCONSISTING OF KYANITE, SILLIMANITE, ANDALUSITE, DUMORTIERITE, TOPAZ ANDMULITE, SAID ALUMINUM SILICATE PARTICLES SERVING AS HEAT INSULATINGBODIES AMONG THE CAST IRON PARTICLES TENDING TO SUPPRESS THE THERMALDECOMPOSING EFFECT OF THE INCANDESCIBLE CAST IRON PARTICLES ON THEORGANIC BINDER MATRIX; AND SAID ORGANIC BINDER MATRIX CONSISTINGESSENTIALLY OF A HEAT STABLE RUBBER.